Turbulent Structures and Flow Instability in Axial/Radial Dual-Stage Swirlers: A Computational Study

Researchers from the University of Science and Technology China have conducted a numerical study using the large eddy simulation (LES) method to investigate the effect of swirl direction on the turbulent structures, vortex breakdown, and pressure fluctuations inside axial/radial dual-stage swirler configurations. The study reveals significant differences in turbulent kinetic energy density, central recirculation zone characteristics, and spectral proper orthogonal decomposition modal analysis at precessing vortex core frequencies between co-swirl and counter-swirl configurations.

Key Takeaways:

• The counter-swirl configuration exhibits higher turbulent kinetic energy density and a more compact central recirculation zone compared to the co-swirl configuration.
• The counter-swirling flow displays an additional 842 Hz frequency associated with Kelvin-Helmholtz instability in the tangential shear layer, indicating more complex turbulent evolution.
• Small-scale vortices densely distributed in the counter-swirl tangential shear layer are conducive to promoting flame perturbations.
• Q-criterion analysis reveals precessing vortex core near the swirler outlet and fragmented vortices in the central recirculation zone for both configurations.
• Proper orthogonal decomposition shows that the co-swirling flow retains higher energy in the first six modes, while counter-swirl energy concentrates in the tangential shear layer with rapid downstream decay.
• Spectral proper orthogonal decomposition modal analysis at precessing vortex core frequencies confirms that the counter-swirl tangential shear layer forms more stable helical structures.

Statistics:

• 686 Hz (PVC frequency) is the dominant frequency of the co-swirling flow due to shear between the main flow and central recirculation zone.
• 842 Hz is the additional frequency associated with Kelvin-Helmholtz instability in the counter-swirling tangential shear layer.
• 6 modes are retained with higher energy in the co-swirling flow proper orthogonal decomposition.

Sources:

• Influence of Co- and Counter-swirl On Flow Instability Inside Axial/radial Dual-stage Swirlers. Physics of Fluids, 2025;37(8).
• Minghou Liu et al., University of Science and Technology China, USTC, Dept. of Thermal Science & Energy Engineering, Hefei 230027, Anhui, People's Republic of China.
• NewsRx LLC, 2025.
• American Institute of Physics, Physics of Fluids, Aip Publishing, 1305 Walt Whitman Rd, Ste 300, Melville, NY 11747-4501, USA.